Fan Assembly and Vacuum Cleaner

ABSTRACT

A vacuum cleaner and a fan assembly that includes a shell, a rotation shaft, a first impeller, a diffuser and a second impeller. The shell includes an air inlet and an air outlet in communication with each other. The rotation shaft is arranged in the shell and extends from the air inlet to the air outlet. The first impeller is arranged on the rotation shaft and located at a side of the air inlet. The diffuser is arranged in the shell and located at a side of the air outlet. The second impeller is arranged on the rotation shaft and located between the first impeller and the diffuser. The fan assembly may reduce working noise of the fan assembly while ensuring an air supply capacity of the fan assembly, and may reduce a radial size of the fan assembly, and may improve gas flow efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of the international patent application No. PCT/CN2021/131381, filed on Nov. 18, 2021, which claims priority to Chinese Patent application No. 202011558784.1 filed at China National Intellectual Property Administration (CNIPA) on Dec. 25, 2020, and entitled “FAN ASSEMBLY AND VACUUM CLEANER”, the contents of which are hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to the technical field of household appliances, and in particular to a fan assembly and a vacuum cleaner.

BACKGROUND

Vacuum cleaners are gradually favored by consumers due to their advantages such as small sizes, light weights, usage convenience, or the like. Improving suction of the vacuum cleaners by increasing rotation speeds or sizes of fans of the vacuum cleaners may cause an increase in noise and volume of the vacuum cleaners.

SUMMARY

A first aspect of the disclosure provides a fan assembly.

A second aspect of the disclosure provides a vacuum cleaner.

The first aspect of the disclosure provides a fan assembly, including a shell, a rotation shaft, a first impeller, a diffuser and a second impeller. The shell includes an air inlet and an air outlet in communication with each other. The rotation shaft is arranged in the shell and extends from the air inlet to the air outlet. The first impeller is arranged on the rotation shaft and located at a side of the air inlet. The diffuser is arranged in the shell and located at a side of the air outlet. The second impeller is arranged on the rotation shaft and located between the first impeller and the diffuser.

The fan assembly provided in the disclosure includes a shell, a rotation shaft, a first impeller, a diffuser and a second impeller. The shell includes an air inlet and an air outlet in communication with each other. The rotation shaft is arranged in the shell and extends from the air inlet to the air outlet. The first impeller and the second impeller are sequentially arranged on the rotation shaft in a direction from the air inlet to the air outlet, and the first impeller, the second impeller may be used in cooperation with the diffuser to drive a gas to go into the shell from the air inlet and go out from the air outlet.

During operation of the fan assembly, the rotation shaft is driven to drive the first impeller and the second impeller to rotate. The first impeller rotates at the air inlet, thereby sucking an external gas into the shell from the air inlet and driving the gas to flow towards the second impeller. After the gas flows to the second impeller, the gas further flows to the diffuser under the drive of the second impeller. In particular, in some embodiments, two-stage driving of the gas is achieved through cooperation of the first impeller and the second impeller, which may improve an air supply capacity of the fan assembly on one hand and may reduce working noise of the fan assembly on the other hand.

Furthermore, the second impeller drives the gas to the diffuser, so that airflow is blown out from the air outlet after it is diffused by the diffuser. In particular, in some embodiments, due to design of the diffuser, radial sizes of the first impeller and the second impeller may be reduced while still ensuring the air supply capacity of the fan assembly, thereby reducing a radial size of the fan assembly itself and achieving miniaturization and compact design of structure of the fan assembly.

In some embodiments, the fan assembly provided in the disclosure may reduce working noise of the fan assembly while ensuring the air supply capacity of the fan assembly through cooperation of the first impeller and the second impeller, and may reduce the radial size of the fan assembly through design of the diffuser. In some embodiments, the radial size of the fan assembly does not increase while ensuring that the fan assembly achieves air supply through two-stage impellers, so that the radial size of the fan assembly provided in the disclosure is similar to that of a fan assembly with a single impeller, and gas flow efficiency may also improve.

The second aspect of the disclosure provides a vacuum cleaner, including the fan assembly according to the first aspect of the disclosure.

The vacuum cleaner provided in the disclosure includes the fan assembly according to the first aspect of the disclosure.

In particular, the vacuum cleaner provided in the disclosure may be a hand-held vacuum cleaner, has structural characteristics of miniaturization, and may be convenient for users to use it.

Additional aspects and advantages of the disclosure will become apparent in the following description sections, or will be understood through practice of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the disclosure will become apparent and readily understood from descriptions of embodiments made in combination with the following drawings, in which:

FIG. 1 is a schematic structural diagram of a fan assembly according to some embodiments of the disclosure;

FIG. 2 is a cross-sectional view of the fan assembly of some embodiments shown in FIG. 1 ;

FIG. 3 is a partial schematic diagram of some embodiments shown in FIG. 2 ;

FIG. 4 is a partial schematic diagram of some embodiments shown in FIG. 2 ;

FIG. 5 is a partial schematic diagram of some embodiments shown in FIG. 2 ;

FIG. 6 is a schematic structural diagram of a backflow structure in the fan assembly of some embodiments shown in FIG. 1 ;

FIG. 7 is a partial schematic diagram of some embodiments shown in FIG. 2 ;

FIG. 8 is a schematic diagram of performance comparison between the fan assembly provided in the disclosure and a fan assembly provided in the related art.

Correspondences between reference symbols and component names in FIG. 1 to FIG. 7 are:

100 shell, 102 first mounting segment, 104 second mounting segment, 106 transition segment, 108 fin, 110 air inlet, 112 air outlet, 114 second arc line, 116 second straight line, 200 rotation shaft, 202 nut, 204 driving member, 300 first impeller, 302 first turntable, 304 first blade, 306 first guidance hood, 400 diffuser, 402 diffusion blade, 500 second impeller, 502 second turntable, 504 second blade, 506 second guidance hood, 600 flow guidance passage, 602 diffusion passage, 604 backflow passage, 700 backflow structure, 702 backflow disk, 704 guide blade, 706 containing groove, 708 arc shape, 710 first arc line, 712 first straight line, 800 flow guidance structure, 900 flow-past passage.

DETAILED DESCRIPTION

In order to enable the above objects, features and advantages of the disclosure to be understood more clearly, the disclosure is further described in detail below in combination with the drawings and specific implementations. It should be noted that embodiments of the disclosure and features in the embodiments may be combined with each other without conflict.

Many specific details are set forth in the following descriptions to facilitate a full understanding of the disclosure. However, the disclosure may also be practiced in other manners different from those described here. Therefore, the scope of protection of the disclosure is not limited by specific embodiments disclosed below.

A fan assembly and a vacuum cleaner provided according to some embodiments of the disclosure are described below with reference to FIG. 1 to FIG. 8 . Arrows in FIG. 2 indicate gas flow direction, a solid line in FIG. 8 indicates relevant data of the fan assembly provided in the disclosure, and a dotted line in FIG. 8 indicates test data of a fan assembly in the related art.

As shown in FIG. 1 and FIG. 2 , some embodiments of a first aspect of the disclosure provide a fan assembly, including a shell 100, a rotation shaft 200, a first impeller 300, a diffuser 400 and a second impeller 500. The shell 100 includes an air inlet 110 and an air outlet 112 in communication with (e.g., in fluidic communication with) each other. The rotation shaft 200 is arranged in the shell 100 and extends from the air inlet 110 to the air outlet 112. The first impeller 300 is arranged on the rotation shaft 200 and located at a side of the air inlet 110. The diffuser 400 is arranged in the shell 100 and located at a side of the air outlet 112. The second impeller 500 is arranged on the rotation shaft 200 and located between the first impeller 300 and the diffuser 400.

The fan assembly provided in the embodiments includes a shell 100, a rotation shaft 200, a first impeller 300, a diffuser 400 and a second impeller 500. The shell 100 includes an air inlet 110 and an air outlet 112 in communication with each other. The rotation shaft 200 is arranged in the shell 100 and extends from the air inlet 110 to the air outlet 112. The first impeller 300 and the second impeller 500 are sequentially arranged on the rotation shaft 200 in a direction from the air inlet 110 to the air outlet 112, and the first impeller 300, the second impeller 500 may be used in cooperation with the diffuser 400 to drive a gas to go into the shell 100 from the air inlet 110 and go out from the air outlet 112.

As shown in FIG. 2 , during operation of the fan assembly, the rotation shaft 200 is driven to drive the first impeller 300 and the second impeller 500 to rotate. The first impeller 300 rotates at the air inlet 110, thereby sucking an external gas into the shell 100 from the air inlet 110 and driving the gas to flow towards the second impeller 500. After the gas flows to the second impeller 500, the gas further flows to the diffuser 400 under the drive of the second impeller 500. In particular, in some embodiments, two-stage driving of the gas is achieved through cooperation of the first impeller 300 and the second impeller 500, which may improve an air supply capacity of the fan assembly on one hand and may reduce working noise of the fan assembly on the other hand.

Furthermore, the second impeller 500 drives the gas to the diffuser 400, so that airflow is blown out from the air outlet 112 after it is diffused by the diffuser 400. In particular, due to design of the diffuser 400, radial sizes of the first impeller 300 and the second impeller 500 may be greatly reduced in case of ensuring the air supply capacity of the fan assembly, thereby reducing a radial size of the fan assembly itself and achieving miniaturization and compact design of structure of the fan assembly.

The fan assembly provided in the disclosure may effectively reduce working noise of the fan assembly while ensuring the air supply capacity of the fan assembly through cooperation of the first impeller and the second impeller 500, and may greatly reduce the radial size of the fan assembly through design of the diffuser 400. In some embodiments, the radial size of the fan assembly may not increase while ensuring that the fan assembly may achieve air supply through two-stage impellers, so that the radial size of the fan assembly provided in the disclosure is similar to that of a fan assembly with a single impeller, and gas flow efficiency may be improved.

In some embodiments of the disclosure, as shown in FIG. 2 , the fan assembly further includes a flow guidance passage 600. The flow guidance passage 600 is provided with two ends in communication with an outlet end of the first impeller 300 and an inlet end of the second impeller 500 respectively, and diameter of at least a part of the flow guidance passage 600 gradually increases in the gas flow direction.

In some embodiments, the fan assembly further includes a flow guidance passage 600. The flow guidance passage 600 is arranged inside the shell 100, an inlet of the flow guidance passage 600 is in communication with the outlet end of the first impeller 300, and an outlet of the flow guidance passage 600 is in communication with the inlet end of the second impeller 500, thereby playing a role of guiding flow between the first impeller 300 and the second impeller 500 and reducing airflow loss.

Furthermore, as shown in FIG. 2 , the diameter of at least a part of the flow guidance passage 600 gradually increases in the gas flow direction. That is, during operation of the fan assembly, airflow entering interior of a flow guidance structure 800 passes through a segment of the flow guidance passage 600 with a gradually increasing diameter. When airflow passes through the part of the flow guidance passage 600 with a gradually increasing diameter, an effect of deceleration and pressurization may be achieved, and noise when the gas flows through the part of the flow guidance passage 600 may be reduced, and airflow pressure may be ensured.

In some embodiments of the disclosure, as shown in FIG. 2 , FIG. 3 and FIG. 4 , the flow guidance passage 600 includes a diffusion passage 602 and a backflow passage 604. The diffusion passage 602 is in communication with the outlet end of the first impeller 300. The backflow passage 604 is in communication with the diffusion passage 602 and the inlet end of the second impeller 500. Diameter of the diffusion passage 602 gradually increases in a gas flow direction.

In some embodiments, the flow guidance passage 600 includes a diffusion passage 602 and a backflow passage 604 in communication with each other. The diffusion passage 602 is in communication with the outlet end of the first impeller 300. The backflow passage 604 is in communication with the diffusion passage 602 and the inlet end of the second impeller 500. As shown in FIG. 3 , according to this design, during operation of the fan assembly, airflow is driven by the first impeller 300, enters the diffusion passage 602 of the flow guidance passage 600 first, then passes through the backflow passage 604 of the flow guidance passage 600, and flows towards the second impeller 500.

In particular, the diameter of the diffusion passage 602 gradually increases in the gas flow direction. That is, when the gas flows in the diffusion passage 602, a flow speed of the gas decreases and air pressure inside the diffusion passage 602 increases. According to this design, a radial size of the first impeller 300 may be effectively reduced in case of ensuring the same air supply volume, thereby achieving compactness and miniaturization of structure of the fan assembly.

In some embodiments, the diffusion passage 602, the backflow passage 604 and the diffuser 400 used in the embodiments are used in cooperation, which may greatly reduce the radial size of the fan assembly, and the radial size of the fan assembly is reduced by 20% compared to a radial size of a fan assembly of a traditional two-stage vacuum cleaner, is equivalent to a radial size of a fan assembly of a single-stage vacuum cleaner, and may improve aerodynamic efficiency compared to the single-stage vacuum cleaner.

In some embodiments of the disclosure, as shown in FIG. 3 , the first impeller 300 is a centrifugal impeller, the diffusion passage 602 includes at least one bend and is located at both sides of the first impeller 300, and the backflow passage 604 is located between the first impeller 300 and the second impeller 500.

In some embodiments, the first impeller 300 is a centrifugal impeller, and the diffusion passage 602 includes at least one bend. According to this design, an axial direction of the first impeller 300 is arranged towards the air inlet 110, so that a radial direction of the first impeller 300 is used as the outlet end. Furthermore, as shown in FIG. 3 , the bend of the diffusion passage 602 is located at a peripheral side of the first impeller 300, thereby ensuring that the diffusion passage 602 is located at both sides of the first impeller 300 and is in communication with the air inlet 110 and the second impeller 500 at both sides of the first impeller 300.

In particular, the diameter of the diffusion passage 602 in the gas flow direction gradually increases, and the diffusion passage 602 itself is configured with bend. According to this design, the diffusion passage 602 integrates diffusion and bending functions together, so that airflow in the diffusion passage 602 may be decelerated and pressurized while turning, thereby reducing the radial size of the first impeller 300.

In some embodiments of the disclosure, as shown in FIG. 1 and FIG. 2 , the fan assembly further includes a backflow structure 700. The backflow structure 700 is arranged in the shell 100 and located between the first impeller 300 and the second impeller 500.

In some embodiments, the fan assembly further includes a backflow structure 700. The backflow structure 700 is arranged in the shell 100 and located between the first impeller 300 and the second impeller 500. The backflow structure 700 is used in cooperation with the first impeller 300, thereby allowing the gas to flow from the first impeller 300 to the backflow structure 700. Specifically, the backflow structure 700 is sleeved on the rotation shaft 200, and plays a role of back flowing the gas blown out radially from the first impeller 300, thereby changing a flow direction of the gas blown out radially from the first impeller 300, so that a part of the gas flows to the second impeller 500.

Specifically, as shown in FIG. 2 and FIG. 3 , when the first impeller 300 is a centrifugal impeller, the first impeller 300 blows out wind radially, and the second impeller 500 is located in the axial direction of the first impeller 300. Therefore, in some embodiments, the backflow structure 700 is used in cooperation with the first impeller 300, so that the backflow structure 700 plays a good role of guiding flow and backflow, and then allowing the gas flows from the first impeller 300 to the second impeller 500.

In some embodiments of the disclosure, as shown in FIG. 4 and FIG. 6 , the backflow structure 700 includes a backflow disk 702 and a guide blade 704. The backflow disk 702 is sleeved on the rotation shaft 200 and has a gap with respect to the rotation shaft 200, and the flow guidance passage 600 is formed between the backflow disk 702 and an inner wall of the shell 100. The guide blade 704 is arranged on the backflow disk 702 and at least partially located in the backflow passage 604.

In some embodiments, the backflow structure 700 includes a backflow disk 702 and a guide blade 704. A radial end surface of the backflow disk 702 is configured as an arc shape 708, so that the backflow disk 702 and interior of the shell 100 define the flow guidance passage 600 together and ensure that the flow guidance passage 600 is in communication with the outlet end of the first impeller 300, thereby allowing the gas driven by the first impeller 300 to flow to the backflow structure 700. Furthermore, the guide blade 704 is at least partially arranged in the backflow passage 604. According to this design, during operation of the fan assembly, the gas enters the flow guidance passage 600 under the drive of the first impeller 300 and flows to the second impeller 500 under a guidance action of the guide blade 704, thereby playing a role of the backflow structure 700 performing good rectification and removing rotation.

Specifically, as shown in FIG. 6 , multiple guide blades 704 are provided and extend spirally along an outer periphery of the backflow disk 702.

Specifically, during operation of the fan, since the first impeller 300 sucks gas in the axial direction and blows out gas in the radial direction, the gas blown out from the first impeller 300 flows towards the inner wall of the shell 100, and the flow direction of the gas blown out from the first impeller 300 is changed through design of the backflow structure 700, especially by cooperation of the flow guidance passage 600 and the guide blade 704, so that the part of airflow flows towards the second impeller 500. Furthermore, there is a gap between the backflow disk 702 and the rotation shaft 200, the backflow disk 702 does not rotate along with the rotation shaft 200 during operation of the fan assembly, the gas blown out from the first impeller 300 has a certain rotation direction itself, and the gas flows in a gap between two adjacent guide blades 704 through design of the guide blades 704, which further plays a role of removing rotation, ensures that the gas smoothly blows to the second impeller 500, avoids phenomenon such as vortex of the gas or the like in a process of the gas flowing to the second impeller 500, and further avoids unnecessary noise generated inside the fan assembly.

In some embodiments, as shown in FIG. 3 and FIG. 5 , a containing groove 706 is arranged at an end surface of the backflow disk 702 facing the air inlet 110, and a first turntable 302 of the first impeller 300 is at least partially accommodated in the containing groove 706, thereby ensuring that the first turntable 302 is arranged to be flush with a part of the backflow disk 702 where the containing groove 706 is not arranged, so that a first guidance hood 306 of the first impeller 300 is arranged to be flush with interior of the shell 100. According to this design, it ensures that the outlet end of the first impeller 300 in the radial direction is aligned with the flow guidance passage 600, each of the first turntable 302 and the first guidance hood 306 is tangent to an inner wall of the flow guidance passage 600, and airflow is not subjected to resistance when the airflow enters interior of the flow guidance passage 600 from the first impeller 300.

In some embodiments of the disclosure, as shown in FIG. 3 , on an axial section of the rotation shaft 200, a radial end surface of the backflow disk 702 is a first arc line 710, a part of the inner wall of the shell 100 forming the diffusion passage 602 is a second arc line 114, a distance between a first circle center O₁ of the first arc line 710 and an axial end surface of the first impeller 300 facing the backflow structure 700 is L1, a distance between a first circle center O₂ of the second arc line 114 and an axial end surface of the first impeller 300 facing the backflow structure 700 is L2.

In some embodiments, on the axial section of the rotation shaft 200, a radial end surface of the backflow disk 702 is a first arc line 710, a part of the inner wall of the shell 100 forming the diffusion passage 602 is a second arc line 114. A diameter of the first arc line 710 is less than that of the second arc line 114, a distance between a first circle center O₁ of the first arc line 710 and an axial end surface of the first impeller 300 facing the backflow structure 700 is L1, a distance between a first circle center O₂ of the second arc line 114 and an axial end surface of the first impeller 300 facing the backflow structure 700 is L2, and they satisfy L1 < L2. According to this design, it ensures that a distance between the first arc line 710 and the second arc line 114 gradually increases in the gas flow direction, that is, it ensures that the diameter of the diffusion passage 602 gradually increases, thereby ensuring that the diffusion passage 602 achieves an effect of deceleration and pressurization on airflow, and reducing the radial size of the first impeller 300.

Specifically, L1 is a distance between the first circle center O₁ and an end surface of the first turntable 302 where a first blade 304 is arranged, and L2 is a distance between the second circle center O₂ and the end surface of the first turntable 302 where the first blade 304 is arranged.

In some embodiments of the disclosure, as shown in FIG. 3 , a distance between a first circle center O₁ and an axial end surface of the first impeller 300 facing the backflow structure 700 is L1, a distance between a second circle center O₂ and an axial end surface of the first impeller 300 facing the backflow structure 700 is L2, and they satisfy 2% (L1-L2)/L1 7%.

In some embodiments, a ratio of a distance L1-L2 between the first circle center O₁ and the second circle center O₂ to the distance L1 between the first circle center O₁ and the axial end surface of the first impeller 300 facing the backflow structure 700 is greater than or equal to 2% and less than or equal to 7%. That is, 2% ≤ (L1-L2)/L1 ≤ 7%. By reasonably designing a positional relationship between the first arc line 710 and the second arc line 114, and variation trend and variation amplitude of the diameter of the diffusion passage 602, it may ensure that the diffusion passage 602 achieves an effect of diffusion and deceleration on airflow, and flow velocity and pressure of airflow in the diffusion passage 602 may be matched with each other, thereby achieving the best effect of diffusion and deceleration, and ensuring an air supply capacity of the first impeller 300 while ensuring the radial size of the first impeller 300.

In some embodiments, (L1-L2)/L1 may take values of 2%, 3%, 4%, 5%, 6%, 7%, etc., which are not specifically limited here. It may be understood by those skilled in the art that any value may be taken, as long as the value ensures the diffusion effect of the diffusion passage 602 on airflow.

In some embodiments of the disclosure, as shown in FIG. 3 and FIG. 4 , on an axial section of the rotation shaft 200, a part of an end surface of the backflow disk 702 forming the backflow passage 604 is a first straight line 712, a part of the inner wall of the shell 100 forming the backflow passage 604 is a second straight line 116, the first straight line 712 is parallel to the second straight line 116 and extends in a radial direction of the rotation shaft 200.

In some embodiments, on the axial section of the rotation shaft 200, a part of an end surface of the backflow disk 702 forming the backflow passage 604 is a first straight line 712, a part of the inner wall of the shell 100 forming the backflow passage 604 is a second straight line 116, the first straight line 712 is arranged to be parallel to the second straight line 116 and extend in a direction towards the rotation shaft 200. According to this design, it ensures that inner walls of the backflow passage 604 are designed in parallel, so that the backflow passage 604 is in cooperation with the guide blades 704 of the backflow structure 700, to achieve an effect of performing rectification and removing rotation on airflow.

Specifically, during operation of the fan, the gas blown out from the first impeller 300 still has a certain rotation direction after entering the backflow passage 604 through the diffusion passage 602, however, the inner walls of the backflow passage 604 are arranged in parallel and in cooperation with the guide blades 704 to work together, to make airflow flow through the gap between two adjacent guide blades 704, thereby playing a certain role of performing adjustment and removing rotation on the airflow, and ensuring that the gas smoothly blows to the second impeller.

In some embodiments of the disclosure, as shown in FIG. 5 , the first impeller 300 includes a first turntable 302, a first blade 304 and a first guidance hood 306. The first turntable 302 is arranged on the rotation shaft 200. The first blade 304 is arranged on an end surface of the first turntable 302 facing the air inlet 110. The first guidance hood 306 is connected to the first blade 304, and the first blade 304 is located between the first turntable 302 and the first guidance hood 306. A distance L3 between an outer edge of the first guidance hood 306 and an axis of the first impeller 300 is greater than a distance L4 between an outer edge of the first turntable 302 and the axis of the first impeller 300.

In some embodiments, the first impeller 300 is a centrifugal impeller and includes a first turntable 302, a first blade 304 and a first guidance hood 306. The first turntable 302 is arranged on the rotation shaft 200 and may drive the first blade 304 to rotate under the drive of the rotation shaft 200. The first guidance hood 306 and the first turntable 302 are located on both sides of the first blade 304 and may play a role of guiding flow during operation, thereby reducing loss of airflow under an action of the first impeller 300. That is, during operation of the first impeller 300, the gas enters interior of the first impeller 300 in the axial direction under the drive of the first blade 304, and is blown out in the radial direction with guidance of the first guidance hood 306 and the first turntable 302.

Furthermore, as shown in FIG. 5 , a distance between an outer edge of the first guidance hood 306 and an axis of the first impeller 300 is L3, a distance between an outer edge of the first turntable 302 and the axis of the first impeller 300 is L4, and they satisfy L3 > L4. That is, at a position of the outlet end of the first impeller 300 in the radial direction, a size of the first guidance hood 306 is longer than that of the first turntable 302. According to this design, it may control airflow to be blown out more evenly and smoothly from the first impeller 300, and may ensure that the airflow blown out from the first impeller 300 has an included angle with respect to the rotation shaft 200 itself, the airflow blown out from the first impeller 300 smoothly enters the flow guidance passage 600, and flow loss and noise generated when the airflow turns in the flow guidance passage 600 are minimum. Based on the above design, the air supply capacity of the fan assembly is ensured on one hand, and noise and loss of the airflow in the flow guidance passage 600 are reduced on the other hand.

In some embodiments of the disclosure, as shown in FIG. 7 , the second impeller 500 includes a second turntable 502, a second blade 504 and a second guidance hood 506. The second turntable 502 is arranged on the rotation shaft 200. The second blade 504 is arranged on an end surface of the second turntable 502 facing the first impeller 300. The second guidance hood 506 is connected to the second blade 504, and the second blade 504 is located between the second turntable 502 and the second guidance hood 506. A distance L5 between an outer edge of the second guidance hood 506 and an axis of the second impeller 500 is greater than a distance L6 between an outer edge of the second turntable 502 and the axis of the second impeller 500.

In some embodiments, the second impeller 500 is a centrifugal impeller and includes a second turntable 502, a second blade 504 and a second guidance hood 506. The second turntable 502 is arranged on the rotation shaft 200 and may drive the second blade 504 to rotate under the drive of the rotation shaft 200. The second guidance hood 506 and the second turntable 502 are located on both sides of the second blade 504 and may play a role of guiding flow during operation, thereby reducing loss of airflow under an action of the second impeller 500. That is, during operation of the second impeller 500, the gas enters interior of the second impeller 500 in the axial direction under the drive of the second blade 504, and is blown out in the radial direction with guidance of the second guidance hood 506 and the second turntable 502.

Furthermore, as shown in FIG. 7 , on a cross section perpendicular to the rotation shaft 200, a distance between an outer edge of the second guidance hood 506 and an axis of the second impeller 500 is L5, a distance between an outer edge of the second turntable 502 and the axis of the second impeller 500 is L6, and they satisfy L5 > L6. That is, at a position of the outlet end of the second impeller 500 in the radial direction, a size of the second guidance hood 506 is longer than that of the second turntable 502. According to this design, it may control airflow to be blown out more evenly and smoothly from the second impeller 500, and may ensure that the airflow blown out from the second impeller 500 has an included angle with respect to the rotation shaft 200 itself, the airflow blown out from the second impeller 500 smoothly enters the diffuser 400, and flow loss and noise generated when the airflow turns are minimum. The air supply capacity of the fan assembly is ensured on one hand, and noise and loss of the airflow in the flow guidance passage 600 are reduced on the other hand.

In some embodiments of the disclosure, as shown in FIG. 7 , on an axial section passing through the rotation shaft 200, a straight line where an extension line of a radial edge of the second turntable 502 is located intersects with an axis of the rotation shaft 200 to form an included angle α which is greater than or equal to 80° and less than or equal to 89°, and the included angle α is located between the second turntable 502 and the air outlet 112.

In some embodiments, on the axial section of the rotation shaft 200, a straight line where an extension line of a radial edge of the second turntable 502 is located forms an included angle α with an axis of the rotation shaft 200, the included angle α is located between the second turntable 502 and the air outlet 112 and is greater than or equal to 80° and less than or equal to 89°, that is, satisfies 80° ≤ α ≤ 89°. According to this design, it ensures that airflow is inclined relative to the rotation shaft 200 after it is blown out from the outlet end of the second impeller 500, and the airflow may smoothly transition into the diffuser 400, thereby reducing airflow loss and airflow noise.

In particular, as shown in FIG. 7 , by setting the distance L5 between an outer edge of the second guidance hood 506 and an axis of the second impeller 500 to be greater than the distance L6 between an outer edge of the second turntable 502 and the axis of the second impeller 500, and by designing the angle α formed between a straight line where an extension line of a radial edge of the second turntable 502 is located and an axis of the rotation shaft 200 to be greater than or equal to 80° and less than or equal to 89°, a technical effect of optimizing two-stage aerodynamic load matching and further improving aerodynamic efficiency of the whole machine may be achieved.

In some embodiments, values taken by the included angle α are not specifically limited, and may be 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, etc. It may be understood by those skilled in the art that any value may be taken, as long as the value may improve aerodynamic efficiency of the whole machine.

In some embodiments of the disclosure, as shown in FIG. 2 , the fan assembly further includes a flow guidance structure 800. The flow guidance structure 800 is arranged on the rotation shaft 200, a flow-past passage 900 is formed between the flow guidance structure 800 and an inner wall of the shell 100 and is in communication with an outlet end of the flow guidance passage 600 and the inlet end of the second impeller 500.

In some embodiments, the fan assembly further includes a flow guidance structure 800. The flow guidance structure 800 is arranged on the rotation shaft 200 and located in the shell 100. A flow-past passage 900 is formed between the flow guidance structure 800 and an inner wall of the shell 100, and both ends of the flow-past passage 900 are in communication with an outlet end of the flow guidance passage 600 and the inlet end of the second impeller 500 respectively. According to this design, it ensures that airflow blown out from the flow guidance passage 600 may flow smoothly to the second impeller 500 under a guidance action of the flow guidance structure 800, obstruction of interior of the shell 100 to the airflow is further reduced, flow speed of the gas inside the shell 100 is ensured on one hand, and flow noise of the airflow in the shell 100 is reduced on the other hand.

In some embodiments of the disclosure, as shown in FIG. 2 , diameter of the flow guidance structure 800 decreases first and then increases in an outflow direction of the flow-past passage 900.

In some embodiments, both ends of the flow guidance structure 800 are connected to the backflow disk 702 and the second impeller 500 respectively in the outflow direction of the flow-past passage 900, and the diameter of the flow guidance structure 800 is ensured to decrease first and then increase. According to this design, it ensures that both ends of the flow guidance structure 800 are tangent to the backflow disk 702 and the second impeller 500 at connections thereof, ensures smooth transition between both ends of the flow guidance structure 800 and the backflow disk 702 and the second impeller 500, avoids existence of steps at the connection of the flow guidance structure 800 and the backflow disk 702 and at the connection of the flow guidance structure 800 and the second impeller 500, and further ensures that airflow gently and smoothly flows from the flow guidance passage 600 to the flow-past passage 900.

In some embodiments of the disclosure, as shown in FIG. 2 , the diffuser 400 is an axial flow diffuser and includes at least one group of diffusion blades 402, and any group of diffusion blades 402 is distributed in an annular shape.

In some embodiments, the diffuser is configured as an axial flow diffuser. The diffuser 400 includes at least one group of diffusion blades 402, and any group of diffusion blades is distributed in an annular shape at the air outlet. According to this design, it ensures that the axial flow diffuser greatly reduces radial sizes of the first impeller and the second impeller on one hand, and ensures air supply efficiency of the fan assembly on the other hand. Furthermore, the axial flow diffuser may be used instead of a radial diffuser, thereby reducing the radial size of the fan assembly.

In some embodiments of the disclosure, as shown in FIG. 2 , the diffuser 400 includes multiple groups of diffusion blades. A number of the diffusion blades 402 gradually increases in a gas flow direction; and/or rotation angles of the diffusion blades 402 gradually decreases in the gas flow direction.

In some embodiments, the diffuser 400 includes multiple groups of diffusion blades 402, and multiple groups of diffusion blades 402 are arranged at intervals in the gas flow direction.

Furthermore, in the gas flow direction, the number of the diffusion blades 402 in each group gradually increases and rotation angles of the diffusion blades 402 in each group gradually decreases. According to this design, the diffusion blades 402 of the diffuser 400 may cooperate with each other to ensure a diffusion effect on airflow. Furthermore, the axial flow diffuser including multiple groups of diffusion blades 402 may be used instead of the radial diffuser, thereby reducing the radial size of the fan assembly.

In some embodiments of the disclosure, as shown in FIG. 2 , the diffusion blade 402 is a ternary blade.

In some embodiments, the diffusion blade 402 is a ternary blade. In particular, multiple diffusion blades 402 may be used in cooperation, and may be used instead of the radial diffuser, thereby reducing the radial size of the fan assembly.

In some embodiments of the disclosure, as shown in FIG. 1 and FIG. 2 , the shell 100 includes a first mounting segment 102, a second mounting segment 104 and a transition segment 106. The first impeller 300 is located in the first mounting segment 102. The second impeller 500 and the diffuser 400 are located in the second mounting segment 104. The transition segment 106 is arranged to be connected to the first mounting segment 102 and the second mounting segment 104.

In some embodiments, the shell 100 includes a first mounting segment 102 a second mounting segment 104 and a transition segment 106 which are connected. The air inlet 110 is arranged on an axial end surface of the first mounting segment 102, and the first impeller 300 is arranged in the first mounting segment 102. The air outlet 112 is arranged at an axial end surface of the second mounting segment 104, and the second impeller 500 is arranged in the second mounting segment 104. The transition segment 106 is arranged between the first mounting segment 102 and the second mounting segment 104, and connected to both the first mounting segment 102 and the second mounting segment 104.

Furthermore, as shown in FIG. 2 , the flow-past passage 900 is formed between the flow guidance structure 800 and an inner wall of the transition segment 106, and the flow guidance passage 600 is formed between a part of an inner wall of the first mounting segment 102 and the backflow disk 702 of the backflow structure 700.

In some embodiments of the disclosure, as shown in FIG. 1 and FIG. 2 , the transition segment 106 is arranged to be recessed towards the rotation shaft 200. The shell 100 further includes fins 108, and the fins 108 are arranged on the transition segment 106 and connected to the first mounting segment 102 and the second mounting segment 104.

In some embodiments, the fan assembly further includes fins 108. The transition segment 106 is arranged to be recessed towards the rotation shaft 200, and the fins 108 are arranged on an outer wall of the shell 100, located at a position of the transition segment 106 and connected to both the first mounting segment 102 and the second mounting segment 104. A heat dissipation area of the fan assembly is effectively increased through arrangement of the fins 108, thereby achieving a purpose of rapid cooling of the fan assembly.

Specifically, the fins 108 are made of an easily thermal-conductive metal material, located between the first impeller 300 and the second impeller 500, and seamlessly connected to the outer wall of the shell 100. Specifically, multiple fins 108 are provided and distributed in an axial direction of the rotation shaft 200.

In some embodiments of the disclosure, as shown in FIG. 1 and FIG. 2 , the rotation shaft 200 is provided with a thread, the fan assembly further includes a nut 202, and the nut 202 is mounted on the thread to fix the first impeller 300.

In some embodiments, as shown in FIG. 1 and FIG. 2 , the fan assembly further includes a nut 202. The rotation shaft 200 is provided with a thread, and installation of the first impeller 300 is achieved by cooperation of the nut 202 and the thread on the rotation shaft 200. Furthermore, a rotation direction of the nut 202 is opposite to that of the rotation shaft 200, to ensure that the first impeller 300 does not fall off during operation of the fan assembly.

In some embodiments of the disclosure, as shown in FIG. 2 , the fan assembly further includes a driving member 204, and the driving member 204 is connected to the rotation shaft 200 and configured to drive the rotation shaft 200 to rotate.

In some embodiments, the fan assembly further includes a driving member 204, and the driving member 204 is connected to the rotation shaft 200 and may drive a rotational operation during operation, thereby allowing the first impeller 300, the second impeller 500 and the diffuser 400 to operate to drive the gas. Specifically, the driving member 204 may use a motor, and the diffuser 400 is arranged on an outer periphery of the driving member 204.

As shown by the arrows in FIG. 2 , in the fan assembly provided in the embodiments, gas flow process is as follows.

The rotation shaft 200 operates, to drive the first impeller 300 and the second impeller 500 arranged on the rotation shaft 200 to rotate. The first impeller 300 rotates to drive the gas outside the shell 100 to enter the shell 100 through the air inlet 110, then the gas part enters the flow guidance passage 600 under the drive of the shell 100, and then passes through the diffusion passage 602 and the backflow passage 604 sequentially. Then, the gas part flows to the flow-past passage 900 with guidance of the guide blade 704, and flows to the second impeller 500 with guidance of the flow-past passage 900. The second impeller 500 continues to drive the gas to flow to the diffuser 400, and finally the gas part passes through the diffuser 400 and flows out from the air outlet 112.

As shown in FIG. 5 , the distance L3 between the outer edge of the first guidance hood 306 and the axis of the first impeller 300 is greater than the distance L4 between the outer edge of the first turntable 302 and the axis of the first impeller 300, which may ensure that a flow field of an outlet end of the first impeller 300 is more uniform, and flow losses of the diffusion passage 602 and the backflow passage 604 are reduced.

As shown in FIG. 3 , the first impeller 300 is a centrifugal impeller, the diffusion passage 602 is provided with a bend, and the diameter of the diffusion passage 602 gradually increases in the gas flow direction, so that airflow may be turned, decelerated and pressurized in the diffusion passage 602, thereby reducing the radial size of the first impeller 300.

As shown in FIG. 4 , the backflow passage 604 is designed in cooperation with the guide blade 704, to achieve an effect of performing rectification and removing rotation on airflow.

As shown in FIG. 2 , the flow guidance structure 800 is arranged on the rotation shaft 200, and a profile of the flow guidance structure 800 is a streamlined profile, and tangent to the first straight line 712 of the backflow disk 702 and the second impeller 500 to achieve smooth transitions.

In some embodiments, as shown in FIG. 7 , the distance L5 between the outer edge of the second guidance hood 506 and the axis of the second impeller 500 is greater than the distance L6 between the outer edge of the second turntable 502 and the axis of the second impeller 500, and on the axial section of the rotation shaft 200, an included angle α formed between the straight line where the extension line of the radial edge of the second turntable 502 is located intersects with the axis of the rotation shaft 200 is greater than or equal to 80° and less than or equal to 89°, which may optimize two-stage aerodynamic load matching and improve aerodynamic efficiency of the whole machine.

As shown in FIG. 1 and FIG. 2 , the diffuser 400 uses a three-stage axial flow diffuser instead of the radial diffuser, thereby reducing the radial size of the fan assembly.

Some embodiments of a second aspect of the disclosure provide a vacuum cleaner, including the fan assembly according to any one of the above embodiments.

The vacuum cleaner provided in some embodiments includes the fan assembly according to any one of the above embodiments. Therefore, the vacuum cleaner has all the advantageous effects of the above fan assembly, which are not elaborated one by one here.

In particular, the vacuum cleaner provided in some embodiments may be a hand-held vacuum cleaner, has structural characteristics of miniaturization, and is convenient for users to use it.

In some embodiments, when the fan assembly provided in some embodiments is applied to the hand-held vacuum cleaner, a large suction operation of the hand-held vacuum cleaner may be achieved due to cooperation of the first impeller 300 with the second impeller 500, thereby improving operation distance and operation effect of the hand-held vacuum cleaner. Furthermore, due to cooperation among multiple components such as the diffusion passage 602, the backflow passage 604, the flow guidance structure 800, the diffuser 400, or the like, a structural size of the hand-held vacuum cleaner is effectively reduced, especially a radial size of the hand-held vacuum cleaner is reduced, which is convenient for users to hold and operate the vacuum cleaner on one hand, and extend the vacuum cleaner into a narrow space to operate on the other hand.

In some embodiments, as shown in FIG. 1 and FIG. 2 , the fan assembly provided in some embodiments includes the first impeller 300, the diffusion passage 602, the backflow passage 604, the rotation shaft 200, the flow guidance structure 800, the second impeller 500, fins 108, the nut 202, the diffuser 400, and other structures. Air passes through the first impeller 300, the diffusion passage 602, the backflow passage 604, the flow guidance structure 800, the second impeller 500 and the diffuser 400 sequentially, to achieve a purpose of pressurization.

As shown in FIG. 1 , FIG. 2 and FIG. 5 , the first impeller 300 is fixed onto the rotation shaft 200 by the nut 202, and the rotation direction of the nut 202 is opposite to that of the rotation shaft 200, to ensure that the first impeller 300 does not fall off during operation. The distance between the outer edge of the first guidance hood 306 and the axis of the first impeller 300 is slightly greater than the distance between the outer edge of the first turntable 302 and the axis of the first impeller 300, to control the flow field of the outlet end of the first impeller 300 to be more uniform, and reduce flow losses of the diffusion passage 602 and the backflow passage 604.

As shown in FIG. 1 , FIG. 2 and FIG. 3 , the diffusion passage 602 is defined by the first arc line 710 of the backflow disk 702 and the second arc line 114 of the inner wall of the shell 100. The first circle center O₁ of the first arc line 710 is not coincide with the second circle center O₂ of the second arc line 114, and the first circle center O₁ of the first arc line 710 is closer to the first turntable 302 of the first impeller 300 in the axial direction than the second circle center O₂ of the second arc line 114. The distance between the first circle center O₁ of the first arc line 710 and the first turntable 302 is L1, the distance between the second circle center O₂ of the second arc line 114 and the second turntable 502 is L2, and they satisfy 2% ≤ (L1-L2)/L1 ≤ 7%. According to this design, the diffusion passage 602 forms a gradually expanding passage, and the diffusion passage 602 itself is provided with a bend, which forms the diffusion passage 602 integrating diffusion and bending together, so that airflow may be decelerated and pressurized while turning, thereby reducing the radial size of the first impeller 300. In some embodiments, values of (L1-L2)/L1 may be selected as 2%, 3%, 4%, 5%, 6%, 7%, etc.

As shown in FIG. 3 and FIG. 4 , the backflow passage 604 is defined by the first straight line 712 of the backflow disk 702 and the second straight line 116 of the inner wall of the shell 100, and is used in cooperation with a backflow coupling 16 and the guide blade 704. The first straight line 712 and the second straight line 116 are vertically parallel to each other and cooperate with the guide blade 704, to achieve an effect of performing rectification and removing rotation on airflow. Specifically, there are multiple guide blades 704 in number, and the guide blades 704 are helically distributed on the backflow disk 702.

As shown in FIG. 2 , the rotation shaft 200 is provided with the flow guidance structure 800 and the thread. The rotation direction of the thread is opposite to that of the rotation shaft 200, to ensure that the first impeller 300 does not fall off during operation. An outer wall of the flow guidance structure 800 is streamlined and tangent to the first straight line 712 of the backflow disk 702 and the second impeller 500 to achieve smooth transitions, so that the flow-past passage 900 is formed between the flow guidance passage 600 and interior of the shell 100, and it ensures that the first impeller 300 is stably mounted on the rotation shaft 200.

In some embodiments, as shown in FIG. 5 , the distance between the outer edge of the second guidance hood 506 and the axis of the second impeller 500 is slightly greater than the distance between the outer edge of the second turntable 502 and the axis of the second impeller 500, and on the axial section of the rotation shaft 200, the straight line where the extension line of the radial edge of the second turntable 502 is located is not perpendicular to the axis of the rotation shaft 200, instead, forms an included angle α with the axis of the rotation shaft 200, and the included angle α is between 80° and 89°, to achieve an effect of optimizing two-stage aerodynamic load matching and improving aerodynamic efficiency of the whole machine. In some embodiments, values of the included angle α may be selected as 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, etc.

As shown in FIG. 1 and FIG. 2 , 27 fins 108 are connected to the first mounting segment 102 and the second mounting segment 104 of the shell 100, to play a role of cooling airflow. The fins 108 are made of an easily thermal-conductive metal material, arranged between the first impeller 300 and the second impeller 500, and seamlessly connected to the shell 100.

As shown in FIG. 1 and FIG. 2 , the diffuser 400 uses a three-stage axial flow diffuser and includes three rows of diffusion blades 402, the three rows of diffusion blades 402 include 11, 15 and 23 diffusion blades in number respectively and are sequentially arranged in the gas flow direction, and a rotation angle of each stage of diffusion blades 402 gradually decreases in the gas flow direction. Specifically, the diffusion blade 402 is a ternary blade.

The fan assembly provided in some embodiments uses a solution of two-stage impellers, which may reduce rotation speeds of the impellers by 33% with the same air volume and wind pressure. In case of the vacuum cleaner, the same suction power may be achieved at a lower rotation speed, which achieves an effect of reducing noise of the vacuum cleaner. Furthermore, some embodiments use the diffusion passage 602, the backflow passage 604 and a three-stage axial flow diffuser, which may greatly reduce the radial size of the multi-stage fan assembly, and the radial size of the fan assembly is reduced by 20% compared to a radial size of a fan assembly of a traditional two-stage vacuum cleaner, is equivalent to a radial size of a fan assembly of a prevailing single-stage vacuum cleaner, and significantly improves aerodynamic efficiency compared to the single-stage vacuum cleaner.

In some embodiments, the radial end surface of the backflow disk 702 on the axial section of the rotation shaft 200 and the part of the inner wall of the shell 100 forming the diffusion passage 602 are not limited to arc lines, and spline curve and Bezier curve may also achieve similar effects. When the spline curve is used, a circle center of the spline curve may be understood as a midpoint of a line connecting two end points of the spline curve. When the Bezier curve is used, a circle center of the spline curve may be understood as a midpoint of a line connecting two end points of the Bezier curve.

In some embodiments, multiple guide blades 704 of the backflow structure 700 may be provided and are not limited to 16 guide blades.

In some embodiments, multiple fins 108 may be provided and are not limited to 27 fins, and shape of the fin 108 is not limited to a sheet shape.

In some embodiments, the diffuser 400 is not limited to configuration of three rows of diffusion blades 402, and diffusion blades 402 are not limited to 11, 15 and 23 diffusion blades in number.

In some embodiments, as shown in FIG. 8 , a solid line in the figure indicates relevant data of the fan assembly provided in some embodiments, and a dotted line in the figure indicates test data of a fan assembly in the related art. It may be seen from FIG. 8 clearly that the fan assembly provided in some embodiments is significantly superior to the related art in terms of air supply capacity, radial size and working noise.

In descriptions of the disclosure, a term “multiple” refers to two or more, and unless otherwise defined explicitly, terms “upper”, “lower” or the like indicate orientation or positional relationships based on orientation or positional relationships shown in the drawings, are only intended to facilitate the descriptions of the disclosure and simplify the descriptions, and are not intended to indicate or imply that a referred device or element must have a particular orientation, configure and operate in a particular orientation, and thus cannot be understood as limitation of the disclosure. Terms “connection”, “mount”, “fix”, or the like shall be understood in a broad sense. For example, “connection” may be a fixed connection, a detachable connection, or an integral connection; may be a direct connection, or an indirect connection through an intermediate medium. Specific meanings of the above terms in the disclosure may be understood by those of ordinary skill in the art according to specific circumstances.

In descriptions of the specification, descriptions of terms “an embodiment”, “some embodiments”, “specific embodiment”, or the like means that specific features, structures, materials or characteristics described in connection with the embodiment or example are included in the embodiment or example of the disclosure. In the specification, schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner.

The above descriptions are only some embodiments of the disclosure, and are not intended to limit the disclosure. For those skilled in the art, there may be various changes and variations in the disclosure. Any modification, equivalent replacement, improvement, or the like made within the spirit and principle of the disclosure shall be included in the scope of protection of the disclosure. 

1. A fan assembly, comprising: a shell, comprising an air inlet and an air outlet in communication with each other; a rotation shaft, arranged in the shell and extending from the air inlet to the air outlet; a first impeller, arranged on the rotation shaft and located at a side of the air inlet; a diffuser, arranged in the shell and located at a side of the air outlet; and a second impeller, arranged on the rotation shaft and located between the first impeller and the diffuser.
 2. The fan assembly of claim 1, further comprising: a flow guidance passage, provided with a first end and a second end in communication with an outlet end of the first impeller and an inlet end of the second impeller, respectively, the flow guidance passage comprising: a diffusion passage, in communication with the outlet end of the first impeller, wherein a diameter of the diffusion passage gradually increases in a gas flow direction; and a backflow passage, in communication with the diffusion passage and the inlet end of the second impeller.
 3. The fan assembly of claim 2, wherein the first impeller is a centrifugal impeller; the diffusion passage comprises at least one bend and is located at both sides of the first impeller, and the backflow passage is located between the first impeller and the second impeller.
 4. The fan assembly of claim 2, further comprising: a backflow structure, arranged in the shell and located between the first impeller and the second impeller, the backflow structure comprising: a backflow disk, sleeved on the rotation shaft, and the flow guidance passage formed between the backflow disk and an inner wall of the shell; and a guide blade, arranged on the backflow disk and at least partially located in the backflow passage.
 5. The fan assembly of claim 4, wherein on an axial section of the rotation shaft, a radial end surface of the backflow disk is a first arc line, a part of the inner wall of the shell forming the diffusion passage is a second arc line, and a distance between a first circle center of the first arc line and an axial end surface of the first impeller facing the backflow structure is less than a distance between a second circle center of the second arc line and an axial end surface of the first impeller facing the backflow structure.
 6. The fan assembly of claim 5, where a ratio of a distance between the first circle center and the second circle center to the distance between the first circle center and the axial end surface of the first impeller facing the backflow structure is greater than or equal to 2% and less than or equal to 7%.
 7. The fan assembly of claim 4, wherein on an axial section of the rotation shaft, a part of an end surface of the backflow disk forming the backflow passage is a first straight line, a part of the inner wall of the shell forming the backflow passage is a second straight line, the first straight line is parallel to the second straight line and extends in a radial direction of the rotation shaft.
 8. The fan assembly of claim 1, wherein the first impeller comprises: a first turntable, arranged on the rotation shaft; a first blade, arranged on an end surface of the first turntable facing the air inlet; and a first guidance hood, connected to the first blade, and the first blade located between the first turntable and the first guidance hood, wherein a distance between an outer edge of the first guidance hood and an axis of the first impeller is greater than a distance between an outer edge of the first turntable and the axis of the first impeller.
 9. The fan assembly of claim 1, wherein the second impeller comprises: a second turntable, arranged on the rotation shaft; a second blade, arranged on an end surface of the second turntable facing the first impeller; and a second guidance hood, connected to the second blade, and the second blade located between the second turntable and the second guidance hood, wherein on a cross section perpendicular to the rotation shaft, a distance between an outer edge of the second guidance hood and an axis of the second impeller is greater than a distance between an outer edge of the second turntable and the axis of the second impeller.
 10. The fan assembly of claim 9, wherein on an axial section passing through the rotation shaft, a straight line where an extension line of a radial edge of the second turntable is located intersects with an axis of the rotation shaft to form an included angle, and the included angle is located between the second turntable and the air outlet.
 11. The fan assembly of claim 2, further comprising: a flow guidance structure, arranged on the rotation shaft, a flow-past passage formed between the flow guidance structure and an inner wall of the shell, and the flow-past passage is in communication with an outlet end of the flow guidance passage and the inlet end of the second impeller, wherein diameter of the flow guidance structure decreases first and then increases in an outflow direction of the flow-past passage.
 12. The fan assembly of claim 1, wherein the diffuser is an axial flow diffuser and comprises at least one group of diffusion blades distributed in an annular shape.
 13. The fan assembly of claim 12, wherein the diffuser comprises a plurality of groups of diffusion blades; a number of the diffusion blades in each group gradually increases in a gas flow direction; and/or rotation angles of the diffusion blades in each group gradually decreases in the gas flow direction.
 14. The fan assembly of claim 1, wherein the shell comprises: a first mounting segment, in which the first impeller is located; a second mounting segment, in which the second impeller and the diffuser are located; and a transition segment, connected to the first mounting segment and the second mounting segment.
 15. The fan assembly of claim 14, wherein the transition segment is arranged to be recessed towards the rotation shaft, the shell further comprises fins arranged on the transition segment and connected to the first mounting segment and the second mounting segment.
 16. The fan assembly of claim 1, wherein the rotation shaft is provided with a thread, and the fan assembly further comprises a nut mounted on the thread to fix the first impeller.
 17. A vacuum cleaner, comprising: the fan assembly of claim
 1. 